Getting clear on climate facts

With the Intergovernmental Panel on Climate Change (IPCC)[2] poised to release its Fifth Assessment of the science underpinning our understanding of climate change, it’s useful to take a step back and recap some of the “big picture” facts.

What is already clear from the science:

Carbon dioxide and other greenhouse gases act to warm the planet.

Carbon dioxide is accumulating in the atmosphere due to emissions from human activities.

The Earth has been warming during the past century. The amount and speed of the warming is unusual compared to past records.

Humans’ emissions of greenhouse gases are largely responsible for this warming.

If emission rates continue, the warming in the 21st century will be much more significant than the warming in the previous century.These facts have been affirmed by all the previous IPCC reports, and scientists’ confidence in these statements[3] has only grown in successive reports. Although the Fifth Assessment will provide additional information about recent observations, and our growing knowledge of the processes that affect the Earth’s climate, we expect these basic facts to be further solidified by Friday’s release.

In addition to these “big picture” points that characterize our understanding of climate change at the global scale, it’s also important to note two other areas where our knowledge has grown:

Many extreme weather events have become more frequent or severe, and we expect many of these trends to continue. Heat waves have become more frequent and severe, while periods of extreme cold have become less frequent. The amount of precipitation falling in the heaviest downpours has increased in many regions.

Sea level rose during the 20th century and we should expect it to rise even more by 2100. Although the upper bound of globally-averaged sea level rise remains difficult to estimate, even small amounts of sea level rise can enhance destructive storm surges that affect coastal communities when tropical or winter storms come ashore.

There is considerable experience and evidence to suggest that we are right to be concerned, given recent billion-dollar damages[4] suffered by communities and businesses from extreme weather. Many large corporations are taking climate-related threats seriously. As identified in our recent Weathering the Storm[5] report, nine out of 10 S&P Global 100 companies see extreme weather as a current or future business risk. The Department of Energy[6] recently identified how our power plants and electricity grid can be compromised by heat waves, lack of reliable water supplies, and coastal storms.

As the IPCC report gives us a comprehensive assessment of existing climate change research, our growing knowledge of extreme events and sea level rise give us a clearer, locally relevant dimension to this global challenge.